CancellationTokenSource.Cancel CancellationTokenSource.Cancel CancellationTokenSource.Cancel CancellationTokenSource.Cancel Method

定义

传达取消请求。Communicates a request for cancellation.

重载

Cancel() Cancel() Cancel() Cancel()

传达取消请求。Communicates a request for cancellation.

Cancel(Boolean) Cancel(Boolean) Cancel(Boolean) Cancel(Boolean)

如果出现异常,传达取消请求,并指定是否应处理其余回调和可取消操作。Communicates a request for cancellation, and specifies whether remaining callbacks and cancelable operations should be processed if an exception occurs.

Cancel() Cancel() Cancel() Cancel()

传达取消请求。Communicates a request for cancellation.

public:
 void Cancel();
public void Cancel ();
member this.Cancel : unit -> unit
Public Sub Cancel ()

异常

聚合异常包含由相关联的 CancellationToken 上已注册的回调引发的所有异常。An aggregate exception containing all the exceptions thrown by the registered callbacks on the associated CancellationToken.

示例

下面的示例使用的随机数生成器来模拟从 11 个不同的 instruments 读取 10 个整数值的数据收集应用程序。The following example uses a random number generator to emulate a data collection application that reads 10 integral values from eleven different instruments. 零值指示度量已失败的一个检测,这种情况下,应取消操作并没有总体平均值应被计算出来。A value of zero indicates that the measurement has failed for one instrument, in which case the operation should be cancelled and no overall mean should be computed.

若要处理可能取消操作,该示例实例化CancellationTokenSource对象,它生成的取消标记传递到TaskFactory对象。To handle the possible cancellation of the operation, the example instantiates a CancellationTokenSource object that generates a cancellation token which is passed to a TaskFactory object. TaskFactory对象又取消将标记传递到每个任务负责收集特定乐器的读数。The TaskFactory object in turn passes the cancellation token to each of the tasks responsible for collecting readings for a particular instrument. TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken)调用方法来确保只有在已成功收集所有读数后计算平均值。The TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken) method is called to ensure that the mean is computed only after all readings have been gathered successfully. 如果某个任务具有不是因为已取消对调用TaskFactory.ContinueWhenAll方法将引发异常。If a task has not because it has been cancelled, the call to the TaskFactory.ContinueWhenAll method throws an exception.

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      // Define the cancellation token.
      CancellationTokenSource source = new CancellationTokenSource();
      CancellationToken token = source.Token;

      Random rnd = new Random();
      Object lockObj = new Object();
      
      List<Task<int[]>> tasks = new List<Task<int[]>>();
      TaskFactory factory = new TaskFactory(token);
      for (int taskCtr = 0; taskCtr <= 10; taskCtr++) {
         int iteration = taskCtr + 1;
         tasks.Add(factory.StartNew( () => {
                                       int value;
                                       int[] values = new int[10];
                                       for (int ctr = 1; ctr <= 10; ctr++) {
                                          lock (lockObj) {
                                             value = rnd.Next(0,101);
                                          }
                                          if (value == 0) { 
                                             source.Cancel();
                                             Console.WriteLine("Cancelling at task {0}", iteration);
                                             break;
                                          }   
                                          values[ctr-1] = value; 
                                       }
                                       return values;
                                    }, token));   
         
      }
      try {
         Task<double> fTask = factory.ContinueWhenAll(tasks.ToArray(), 
                                                      (results) => {
                                                         Console.WriteLine("Calculating overall mean...");
                                                         long sum = 0;
                                                         int n = 0; 
                                                         foreach (var t in results) {
                                                            foreach (var r in t.Result) {
                                                                  sum += r;
                                                                  n++;
                                                               }
                                                         }
                                                         return sum/(double) n;
                                                      } , token);
         Console.WriteLine("The mean is {0}.", fTask.Result);
      }   
      catch (AggregateException ae) {
         foreach (Exception e in ae.InnerExceptions) {
            if (e is TaskCanceledException)
               Console.WriteLine("Unable to compute mean: {0}", 
                                 ((TaskCanceledException) e).Message);
            else
               Console.WriteLine("Exception: " + e.GetType().Name);
         }
      }
      finally {
         source.Dispose();
      }
   }
}
// Repeated execution of the example produces output like the following:
//       Cancelling at task 5
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 10
//       Unable to compute mean: A task was canceled.
//       
//       Calculating overall mean...
//       The mean is 5.29545454545455.
//       
//       Cancelling at task 4
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 5
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 6
//       Unable to compute mean: A task was canceled.
//       
//       Calculating overall mean...
//       The mean is 4.97363636363636.
//       
//       Cancelling at task 4
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 5
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 4
//       Unable to compute mean: A task was canceled.
//       
//       Calculating overall mean...
//       The mean is 4.86545454545455.
Imports System.Collections.Generic
Imports System.Threading
Imports System.Threading.Tasks

Module Example
   Public Sub Main()
      ' Define the cancellation token.
      Dim source As New CancellationTokenSource()
      Dim token As CancellationToken = source.Token

      Dim lockObj As New Object()
      Dim rnd As New Random

      Dim tasks As New List(Of Task(Of Integer()))
      Dim factory As New TaskFactory(token)
      For taskCtr As Integer = 0 To 10
         Dim iteration As Integer = taskCtr + 1
         tasks.Add(factory.StartNew(Function()
                                       Dim value, values(9) As Integer
                                       For ctr As Integer = 1 To 10
                                          SyncLock lockObj
                                             value = rnd.Next(0,101)
                                          End SyncLock
                                          If value = 0 Then 
                                             source.Cancel
                                             Console.WriteLine("Cancelling at task {0}", iteration)
                                             Exit For
                                          End If   
                                          values(ctr-1) = value 
                                       Next
                                       Return values
                                    End Function, token))   
         
      Next
      Try
         Dim fTask As Task(Of Double) = factory.ContinueWhenAll(tasks.ToArray(), 
                                                         Function(results)
                                                            Console.WriteLine("Calculating overall mean...")
                                                            Dim sum As Long
                                                            Dim n As Integer 
                                                            For Each t In results
                                                               For Each r In t.Result
                                                                  sum += r
                                                                  n+= 1
                                                               Next
                                                            Next
                                                            Return sum/n
                                                         End Function, token)
         Console.WriteLine("The mean is {0}.", fTask.Result)
      Catch ae As AggregateException
         For Each e In ae.InnerExceptions
            If TypeOf e Is TaskCanceledException
               Console.WriteLine("Unable to compute mean: {0}", 
                                 CType(e, TaskCanceledException).Message)
            Else
               Console.WriteLine("Exception: " + e.GetType().Name)
            End If   
         Next
      Finally
         source.Dispose()
      End Try                                                          
   End Sub
End Module
' Repeated execution of the example produces output like the following:
'       Cancelling at task 5
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 10
'       Unable to compute mean: A task was canceled.
'       
'       Calculating overall mean...
'       The mean is 5.29545454545455.
'       
'       Cancelling at task 4
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 5
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 6
'       Unable to compute mean: A task was canceled.
'       
'       Calculating overall mean...
'       The mean is 4.97363636363636.
'       
'       Cancelling at task 4
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 5
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 4
'       Unable to compute mean: A task was canceled.
'       
'       Calculating overall mean...
'       The mean is 4.86545454545455.

注解

关联CancellationToken将通知的取消操作并将转换为状态其中IsCancellationRequested,则返回 true。The associated CancellationToken will be notified of the cancellation and will transition to a state where IsCancellationRequested returns true.

与注册的任何回调或可取消操作CancellationToken将执行。Any callbacks or cancelable operations registered with the CancellationToken will be executed.

我们建议可取消操作和回调注册与CancellationToken不会引发异常。We recommend that cancelable operations and callbacks registered with CancellationToken not throw exceptions.

取消此重载将聚合到引发的任何异常AggregateException,这样,一个回调引发异常不会阻止其他已注册的回调正在执行。This overload of Cancel will aggregate any exceptions thrown into an AggregateException, such that one callback throwing an exception will not prevent other registered callbacks from being executed.

另请参阅

Cancel(Boolean) Cancel(Boolean) Cancel(Boolean) Cancel(Boolean)

如果出现异常,传达取消请求,并指定是否应处理其余回调和可取消操作。Communicates a request for cancellation, and specifies whether remaining callbacks and cancelable operations should be processed if an exception occurs.

public:
 void Cancel(bool throwOnFirstException);
public void Cancel (bool throwOnFirstException);
member this.Cancel : bool -> unit
Public Sub Cancel (throwOnFirstException As Boolean)

参数

throwOnFirstException
Boolean Boolean Boolean Boolean

如果异常应立即传播,则为 true;否则为 falsetrue if exceptions should immediately propagate; otherwise, false.

异常

聚合异常包含由相关联的 CancellationToken 上已注册的回调引发的所有异常。An aggregate exception containing all the exceptions thrown by the registered callbacks on the associated CancellationToken.

注解

关联CancellationToken将通知的取消操作并将转换为状态位置IsCancellationRequested返回trueThe associated CancellationToken will be notified of the cancellation and will transition to a state where IsCancellationRequested returns true.

与注册的任何回调或可取消操作CancellationToken将执行。Any callbacks or cancelable operations registered with the CancellationToken will be executed. 将按后进先出顺序以同步方式执行的回调。Callbacks will be executed synchronously in LIFO order.

我们建议可取消操作和回调注册与CancellationToken不会引发异常。We recommend that cancelable operations and callbacks registered with CancellationToken not throw exceptions.

如果throwOnFirstExceptiontrue,对的调用将立即传播异常Cancel,阻止其余回调和从正在处理的可取消操作。If throwOnFirstException is true, an exception will immediately propagate out of the call to Cancel, preventing the remaining callbacks and cancelable operations from being processed.

如果throwOnFirstExceptionfalse,此重载将聚合到引发的任何异常AggregateException,这样,一个回调引发异常不会阻止其他已注册的回调正在执行。If throwOnFirstException is false, this overload will aggregate any exceptions thrown into an AggregateException, such that one callback throwing an exception will not prevent other registered callbacks from being executed.

另请参阅

适用于